1. Technical Field of the Invention
The present invention relates to component mounting method and apparatus wherein a component is mounted on a mounting surface by bonding their respective metallic electrical bonding interconnects. In particular, it describes the process of and apparatus for manufacturing an electronic circuit substrate wherein electronic components such as bare IC chips are mounted on substrates such as printed-wiring circuit boards.
2. Description of Prior Art
Bare IC chips are formed of a semiconductor wafer on which circuit patterns are fabricated using thin-film forming techniques and mounted on a printed board for manufacturing an electronic circuit board. As shown in FIG. 11, electrodes 107 are prefabricated in a circuit pattern on a bare IC chip 103 to be electrically connected to conductor lands 109 formed on a printed-wiring board 104. For mounting such bare IC chip 103 on the circuit board 104, a surface mount method is used wherein the bonding face 103a of the IC chip 103 where the electrodes 7 exist and the bonding face 104a of the circuit board 104 where the conductor lands 109 exist are brought to a face-to-face contact and fixed to each other for achieving electrical connection between the conductor lands 109 and electrodes 107. Sealant 111 made of resin is then filled between the bonding faces 103a, 104a as shown in FIG. 12 for encapsulating the circuit pattern including the electrical bonding areas formed on the bonding face 103a of the IC chip 103.
In a mounting method which has been used in recent years, a bare IC chip 103, on which metal bumps 108 have been formed upon electrodes 107 as shown in FIG. 11 by a wire bonding process or the like, is held by suction with a suction nozzle 114 and is brought opposite to a circuit board 104 at a predetermined location, where the bumps 108 are pressed onto conductor lands 109 on the circuit board 104 for bonding them in electrical connection with each other. At the same time the bumps 108 and conductor lands 109 are fixed to each other with adhesive 112 that may be supplied in advance to bumps 108 or conductor lands 109 or with solder paste that assists electrical bonding of metal interconnects. The bare IC chip 103 is thus mounted on the circuit board 104. The circuit board 104 is then held in an inclined state as shown in FIG. 12, and sealant 111 is flowed between the bonding faces 103a, 104a of the IC chip 103 and circuit board 104 as shown in phantom lines in the figure with the use of a dispenser 115 or the like. Sealing is completed when the sealant 111 is filled between the IC chip 103 and circuit board 104 as shown in solid lines in FIG. 12.
In such method the equipment cost is high, since the process of mounting bare IC chips 103 on circuit boards 104 and the process of dispensing sealant 111 between the bonding faces 103, 104a of IC chip 103 and circuit board 104 differ substantially from each other in the handling of circuit boards and the design of operations, and are performed separately in different apparatuses. Moreover, the sealant 111 takes time to flow into between the bonding faces 103, 104a, wherefore the productivity is low. For example, in the case of mounting an IC chip 103 of 10 mm.times.10 mm size, the dispenser 115 is moved along the upper side of the IC chip from one end to another and returned so as to apply the sealant 111 to the entire area between the bonding faces 103a, 104a. The operation is finished only when the sealant has filled between IC chip 103 and circuit board 104 to the extent that a wetted portion 113 is formed around the IC chip 103 as shown in FIG. 12. In such method it takes about 10 seconds for the operation of mounting one IC chip 103. Furthermore, there is not much choice of sealing materials, i.e., the sealant 111 must have a viscosity in the range 2000 to 3000 cps, since it is poured into the very small gap of about 50 .mu.m between the bonding faces 103a, 104a. Moreover, a sealant 111 having such viscosity needs to be heated at a relatively high temperature of from 40 to 60.degree. C. to set, because of which the operation time is further increased. It is also undesirable in the interest of economy in energy since heat consumption is high.
In addition, there is a risk that fillers contained in the sealant 111 that is poured in between the bonding faces 103a, 104a may be distributed in stripes, causing a sealing failure. Also, since electrical connection between bumps 108 of IC chips 103 and conductor lands 109 of circuit boards 104 is accomplished only by mutual contact, a defective bond is sometimes formed, even though the electrical bonding areas on IC chips and circuit boards are fixed with each other with adhesive 112 and sealant 111. The yield of product is thereby decreased. The bumps 108 and lands 109 may be fixed with each other using solder paste, which will, however, result in consumption of more heat and time for heating solder paste and for letting it set.